Anger, and the expression or repression of anger, are considered topics of special relevance to those concerned with mental health, and yet investigators of early emotional development have failed to produce a single study of anger in infancy in the last 40 years. The objectives of the present study are (l) to trace the development of angry behavior throughout the first year of life, describing its form, object, intensity, activators and apparent terminators, and (2) to denote individual differences in these aspects of angry behavior and in the relationships among them. Individual differences will be further related (3) to maternal behavior surrounding the event, and (4) to individual differences in angry and avoidant behavior shown toward the mother in a controlled strange situation observation of separation and reunion in this same sample. It is expected that strong anger toward the mother shown in the home will be associated with affectless avoidance of the mother on reunion in the strange situation, and this is suggestive of repression. The study takes advantage of extensive narrative records obtained from a study of mother-infant interaction in 26 dyads observed in the home for over 1000 hours throughout the first year of life. The study focuses upon episodes of clearly defined angry behavior: More subjective assessments are avoided. The proposed study will serve not merely as a pioneering study of the development of angry behavior, but will also be of immediate use to investigators who wish to assess and interpret the social-emotional functioning of one-year-olds seen in this commonly used laboratory observation.